Before the review, I would like to thank Harold and Chris @ HPA for all the help and installation of these parts. HPA has been so helpful in the modification of my e90 and without Harold's help I would not be as knowledgable as I am now regarding the capabilities of my car.

Before:
As you all know, KW suspension has been a leader in the coil-over market and is usually the first to be suggested to people looking for a drop or upgrade in performance. I loved my KW V2s when they were installed because they were extremely smooth around such rough roads in SoCal and they were on the cheaper side of coil-over kits. I happened to get mine for wholesale and therefore got a tremendous deal.

In respect to performance, I would give them (unmodified) a 4/10 with stock control arm and other such suspension components. The disappointment came when I first took my car to an autocross, where handling is the most important (with braking being second) aspect that will determine posting good numbers. I was confident when i showed up that my KW suspension would give me a significant edge over the competition. I did post up good numbers, however I was extremely disappointed in the performance of the V2s. The car had a ridiculous amount of understeer and really added seconds to my run.

I approached Harold with this issue and he chuckled and responded that KWs (unless they are V3s or Club Sports) are not very performance oriented at all. The problem lies within the progressive springs that come with the V2s. Having progressive springs means that the spring rate is not constant (linear) throughout the spring itself, and thus the ride is softer and is not able to handle the harsh cornering. In retrospect, a linear spring would eliminate most of the understeer.

This is when I was introduced to SWIFT, a leading competitor in the spring world. I read a post submitted by Tyler (who works at HP) on e46fanatics that compared the SWIFT spring to the progressive springs. What a difference! Compression and other qualities were significantly better.

I knew that I wanted the conversion after I saw the post and talked to harold for nearly an hour regarding the positives and negatives of the conversion. I decided on 400/800 spring rates, which is a perfect combination of track/street (more track oriented). In addition, I decided to add camber plates and the whole front M3 conversion. The camber plates would SIGNIFICANTLY help on the track and the M3 control arm kit and strut tower brace would give better feedback and stability in corners.

After:
The results are incomprehensible. When I first picked up the car I noticed a slightly harsher ride on city roads, but not enough to complain. The best way to explain it is that you can really feel the road composition through the steering wheel. There is more vibration in the steering wheel, which I actually love. The car is 1000% more responsive even on the streets. Turning is now confident and very sturdy, as before it was sort of mushy and unresponsive, catering to smoothness over accuracy.

In terms of the twistys, lets not even get me started. As soon as I hit a couple turns in the e90 with these modifications it instantly brought a smile to my face. I fell in love with my car again. The KW suspension, as stated above, was mushy and inaccurate, where as the spring keep you firm and confident around corners. Body roll is limited, stability is increased, and overall feedback is better. The car is so much more predictable and responsive to your commands. I know this is hard to put into words but if I had to start modifications all over again I would definitely throw a great suspension on first. Speed is fun but gets boring. Swinging through corners at a somewhat high (but safe) velocity is way more invigorating.

In conclusion, this conversion is not for everyone. The ride is harsher and road bumps do become rather vocal through your seat and steering wheel. However, the driving experience is heightened immeasurably, and for that reason I highly recommend this conversion. Although I do not have experience with other springs as an option, I trust harold and his opinion. If anyone in SoCal is interested, I would be happy to let you test out the springs for yourself.

I only have a couple weeks of experience with the springs, but I absolutely love them and am confident that you would to. Please contact Harold for any further questions. Hopefully this review sheds some light!

Nice review. I've got the HPA Koni Coilovers with 336/672 Swiftsprings, along with all the M3 suspension bits and I agree with everything you said. My setup is a little more biased to the street and the rough, pot holed excuses for roads here in NY. I did M3 Sways, M3 rear arms, subf-rame bushings and LSD but not strut brace or camber plates. I think the spring really are the key with their reduced weight and linear rate, they just perform extremely well. Harold at HPA really helped me out in making my decisions, had them installed locally since I'm on the east coast.